The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
In automotive transmission art, the dual clutch transmission (DCT) is a relatively new concept. A typical dual clutch transmission configuration includes a pair of mutually exclusively operating input clutches which drive a pair of input shafts. The input shafts may be disposed on opposite sides of an output shaft or may be disposed concentrically between spaced-apart output shafts. One of each of a plurality of pairs of constantly meshing gears which provide the various forward and reverse gear ratios is freely rotatably disposed on one of the shafts and the other of each pair of gears is coupled to one of the other shafts. A plurality of synchronizer clutches selectively couple the freely rotatable gears to the associated shaft to achieve forward and reverse gear ratios. After the synchronizer clutch is engaged, the input clutch associated with the input shaft having the engaged synchronizer clutch is applied to transmit power through the transmission. Reverse gear is similarly achieved except that it includes an additional (idler) gear to provide torque reversal.
Dual clutch transmissions are known for their sporty, performance oriented operating characteristics which mimic those of a conventional mechanical (manual) transmission. They also typically exhibit good fuel economy due to their good gear mesh efficiency, ratio selection flexibility, reduced clutch losses and the lack of a torque converter.
There are, however, design considerations unique to dual clutch transmissions. For example, because of heat generated during clutch slip, the input clutches must be of relatively large size. Furthermore, such heat generation typically requires correspondingly larger and more complex cooling components capable of dissipating relatively large quantities of heat. Finally, because such transmissions typically have many sets of axially aligned, meshing gears, their overall length may limit their use to certain vehicle designs.
Control of the input clutches and selection and engagement of a particular gear by translation of a synchronizer and associated positive clutch is typically achieved by a hydraulic control system. Such a system, itself under the control of an electronic transmission control module (TCM), includes hydraulic valves and actuators which engage the synchronizers and gear clutches. Optimum operating efficiency and thus fuel efficiency and minimal heat generation can be achieved by designing such hydraulic control systems to exhibit low leakage and positive control characteristics. The present invention is so directed.